Compressor



Patented May 30, 1950 UNITED STATES PATENT OFFICE COMPRESSOR Allen Trask, Chicago, Ill.

Application March 16, 1946, Serial No. 654,941

2 Claims.

The present invention relates to compressors `and particularly to multistage compressors wherein a centrifugal compressor means effects one stage of compression and a reciprocating piston type compressor effects a second stage.

One object of the present invention is to reduce to a minimum the size, weight and number of cylinders of a compressor required to create given compression conditions. This is accomplished by increasing the volumetric efciency of compressors and this increase in efficiency constitutes a further object of the invention.

Reciprocating compressors pumping gaseous fluids which are introduced into the suction side of the compressors at one atmosphere require about one-half of their cylinder displacement in order to increase the fluid pressure one atmosphere. A large number of compressors, such as those used for compressing air and refrigerant fluids operate with a discharge pressure of about eight atmospheres. When a single stage reciproeating compressor is working at approximately eight atmospheres then about 50% of the compressor displacement is therefore doing less than 15% of the work required of the compressor. The first one-half of each piston stroke increases the cylinder pressure only one-seventh of the required increase that must be effected during the entire full stroke of the piston.

The present invention provides a relatively simple device wherein a first compression stage is adapted to raise the pressure of the fluid to one atmosphere of compression so that the intake of the reciprocating compressor receives iluid at this elevated pressure. This results in a reduction by one-half of the required displacement and proportionate size of the reciprocating mechanism.

The foregoing constitute some of the principal objects and advantages of the present invention, others of which will be made apparent in the following description and in the drawings, in which,

Fig. 1 is a vertical, sectional view through a compressor embodying the present invention, the view being shown partially in elevation;l

Fig. 2 is a vertical, sectional view through the rotor of Fig. 1, the view being taken on the line 2-2 of Fig. 1;

Fig. 3 is a side elevational view of the rotor shown in Fig. 2, the view showing the complete rotor however, rather than merely that portion shown in Fig. 2; and

Fig. 4 is a fragmentary, longitudinal, sectional view through the cylinder piston portion of the reciprocating compressor showing the piston mounted therein and the crank and connecting 2 rod, the view being taken on the line 4--4 of Fig. 1.

For purposes of illustration a specific embodiment of the present invention has been. selected. It is recognized, of course, that many modifications wll occur to the man skilled in the art and it is intended that such modifications may be made without departing from the scope of the invention.

Referring to the drawings and particularly to Fig. 1 the invention is shown in the form of a compressor housing I5 in which is mounted a shaft I6 that is journaled at Il and I8. The shaft I6 supports a rotor generally indicated at I9.

The housing I5 is provided on one Wall with an outwardly projecting boss 22 that is apertured as at 2| to receive an inlet tube or pipe 22 that passes through a central passage in a bushing 23 that is threaded into the passage 2 I.

Projecting outwardly from the opposite wall of the housing I5 is a boss 25 that is hollow to provide a chamber 26. This chamber is closed by a removable plate 2`I fastened as at 28 by means of screws or the like to the boss 25. A gasket 29 is inserted between the cover plate 2l and the boss 25. The journal bearing I 8 is formed on this last mentioned Wall of the housing I5.

The shaft I6 is provided at one end with a longitudinal passage 30 that extends throughout a portion of its length. At the opposite end of the shaft a shoulder 3I is provided and the shaft projects through an opening 32 in the cover plate 21.

Between the shoulder 3! of the shaft I6 and the cover plate 2l is a sealing member generally indicated at 33, the details and operation of which form no part of the present invention, but are described in detail and claimed in the applicants `copending application, Serial No. 642,286 filed January 19, 1946. It is sufficient to state herein that this sealing member 33 cooperates with a gasket 34 and the shoulder 3| in response to the pressure exerted on the opposite end of the shaft by a compression spring 35 to eiiectively seal the opening 32 through the cover plate 21. This compression spring 35 is seated between the end of shaft I6 and the inner end of the bushing 23 and the amount of compression can be regulated by manipulation of the bushing 23.

The rotor I9 comprises a pair of plates 43 and 44 that sandwich therebetween disc-like members 45 that fit into radial passages 42 formed between the cooperating plates 43 and 44. A plurality of bolts and nuts indicated at 4B hold together the plates 43 and 44 and the disc-like members `45.

The cooperating plates 43 and 44 are provided with hub portions 41 and 48 respectively for iiuid tight mounting on the shaft I6. The rotor may be fixed to the shaft I6 by means of a pressed fit and locked by means of a suitable machine screw 49 that passes through the hub portion 41 and is recessed into a depression in the shaft I6.

The disc portions 45 of the rotor I9 may be separate members as indicated in Fig. 2 or they may be formed in some other suitable manner as is brought out more fully in applicants copending application, Serial No. 634,650 led December 13, 1945. In this last mentioned copending application the details of various other embodiments for the rotor I9 are clearly brought out but for present purposes it is thought that one form only need be shown since the rotor per se does not constitute the present invention.

The discs 45 may be of a material such as wire mesh, glass cloth woven from glass iiber, or sinered metal particles formed in a unitary porous mass, all of which materials provide a plurality of cavities or interstices that are more or less interconnected.,

As shown in Fig. 3 the cooperating plate 44 is provided with projecting portions 53 that correspond in shape with the passages 42 on the Icooperating plate 43 and when the cooperating plates 43 and 44 are bolted together these projections 53 t into the passages 42 so as to provide radial slots in which the discs 45 are held. Thus a multitude of small tortuous passages are provided from a central opening 5! of the rotor I9 to the lperiphery of the rotor through the discs 45.

As noted in Fig. l the passage 30 disposed in one end of the shaft I6 enters the central opening 5I in the rotor I9. In this operation the rotor I9 is caused to rotate with the shaft I6 by a motor (not shown) and gaseous fluid such as Freon enters the hollow portion 30 of the shaft I6 through the inlet pipe 22. This fluid from the hollow portion 30 of the shaft passes into the central opening 5I of the rotor I9 and then is thrown by centrifugal force outwardly through the minute passages formed in the radial ports 42.

The gaseous ilud thus flowing outwardly from the central opening through the porous inserts accumulates diiierent increments or" pressurerin- `duced by centrifugal force as it passes in series from one internal cavity to the next through the connected openings. These successive cavities provide in effect successive stages of compression, each having a higher fluid pressure within than the next adjacent cavity that isdisposed toward the center of the rotor.

In this manner the rst stage compression is completed and the gas thus compressed is discharged from the rotor I9 into the housing I5.

Referring again to Fig. l a reciprocating compressor is generally indicated at 54 and serves as a second stage compressor for the multistage unit. This reciprocating compressor comprises a cylinder 55 that is formed in the one wall of the 'housing I5 and opens at one end into the interior of the housing I5.

The other end of the cylinder 55 is provided with an end wall generally indicated at 56 having a valve port 51 extending therethrough that is adapted to be selectively opened or closed by a reed ap valve member 58. The reed portion of `this flap valve is shown at 59and is movable away from the port 51. A passage or discharge pipe 60 is adapted to communicate with the valve port '51 when the reed 59 is disposed away from the port 51.

In the cylinder 55 is mounted a piston 6I that is adapted to reciprocate under the influence of power directed to the piston through a suitable connecting rod 62 that has at its free end a crank or eccentric 62a that is mounted directly on the shaft I6.

This piston 6I is provided with a piston head 63 having a at outer surface 54 that provides a valve seat for a disc-like valve member 65. This disc-like valve member 65 is provided at its center with a perforation through which passes the shank of a valve button 66. This shank may be riveted over and thus secured to the piston head 63. The piston head is provided on its outer surface 64 with an annular groove 19 and a plurality of openings or valve ports 1I pass through the valve head 63 to place the interior of the piston 6I into communication with the annular groove 10. 'Ihe'relative locations of this groove 10 and the ports 1I in the valve head 63 may be varied as brought out more clearly in applicants copending application Serial No. 626,535 iiled November 3, 1945. LikewiseV though the valve 65 is shown with-,its concave face adjacent to the end wall of piston head 53 it is recognized that this valve may be disposed with its concave face directed away from the end wall or piston head 63. Inasmuch as the specic details of this valve per se do not constitute the present invention further details thereof are not present herein but can be obtained by reference to applicants copending case.

During rotation of the shaft I5 the piston 6I is caused to reciprocate in an upward and downward direction in cylinder 55. During the downward movement of the :piston 6I the disc valve 65 assumes the position shown in Fig. 4 and since this disc valve 65 is provided with a plurality of ports 12 therein uid that is disposed under pressure in the housing I5 passes from underneath the piston 6I through ports 1I and 12 into the cylinder 55. During this downward movement of the piston 6I the reed flap valve 59 effectively covers the port 51.

When the piston 6I reaches this lowermost position and starts its motion upwardly the fluid in the cylinder 55 creates suiiicient pressure against the outer face of the disc valve 65 so as to iiatten this valve against the valve seat 64 thereby covering the ports 1I in the piston head and finally the fluid in the cylinder. Thus during the remainder of the stroke of the piston 6I the uid is compressed in the cylinder until a predetermined pressure is reached at which time the reed flap valve 59 is caused to open and com pressed :duid is allowed to pass through port 51 into the discharge pipe 59. For further details o f the operation of the reciprocating compressor reference may be had to applicants copending application Serial No. 626,535.

The present invention is applicable to high speed reciprocating compressors operating in the range of 1725 R. P. M., the speed of a standard four pole, 60 cycle induction motor. A first stage of compression is effected by the centrifugal compressor rotor I9 which discharges the re.- frigerant at an elevated pressure into the housing I5. This elevated pressure for purposes of illustration may be two atmospheres so that the intake side of the reciprocating compressor 54 receives the refrigerant at two atmospheres of pressure. The size of the centrifugal rotor I9 is substantially proportional to the work it accomplishes and -in this instance it adds approximately 15% to the total overall compressor .size

instead of approximately 50% which would be required in the case of a standard single stage reciprocating compressor for raising the pressure of the refrigerant one atmosphere of pressure.

This invention is particularly Well adapted to low temperature refrigerant compressors. Large compressor displacements are necessary for producing temperatures that are below zero where standard refrigerants such as Freon are used. The use of this invention makes it possible to use smaller refrigeration compressors than could otherwise be used for low temperature work.

A further advantage of the present invention as it is applied to refrigeration compressors is gained through the fact that reduced compressor displacements require less starting torque in the compressor motors. The motors must be powered with starting torques sufficient to start refrigeration compressors under the worst conditions that may exist under abnormal conditions. One example of such condition is where very high suction pressures are encountered. The torque requirements are directly proportional to the compressor displacement. Thus a compressor displacement reduced by one-half through the use of this invention reduces also by one-half the motor starting torque requirement.

In the refrigeration industry motors selected to provide adequate starting torque for meeting all abnormal field conditions are often of oversize horsepower rating based on full load running conditions. For instance, the starting torque of a H. P., 3 phase, squirrel cage induction motor may be required to meet the possible abnormal starting conditions of a frozen food locker plant compressor operating under a normal full load of 6 H. P. By the use of this invention a compressor of smaller displacement could be used and a 71A; H. P. motor of the same type would be fully adequate for the small load as Well as for any abinormal starting demands.

Compressors designed to include the present invention and its advantages may have their size and displacement reduced by a reduction of one or more of the following factors:

1. Piston stroke,

2. Piston diameter, and

3. Number of cylinders.

It is well understood in the art of compressor design that piston head clearance at the end of a compression stroke must be at a minimum to reduce re-expansion losses of compressed fluid that is not forced past the discharge valve. This re-expansion reduces the volumetric eiiiciency of a compressor so that the lower the suction pressure the greater is the re-expansion of the clearance fluid and hence the greater is the loss in volumetric capacity. This invention increases the minimum suction pressure of a compressor and by so doing it increases its volumetric eiliciency under conditions otherwise equal.

I claim:

l. A multistage compressor comprising a chamber, a centrifugal compressor in the chamber and having an intake side and a discharge side, and a reciprocating compressor, a rotatably driven shaft, both compressors being operu atively connected to said shaft, the centrifugal compressor comprising a rotor, a central charnber in the rotor forming the intake side and being sealed from the rst mentioned chamber, and radial passages extending from theI central chamber to the periphery of the rotor, said passages being in the form of interconnecting voids between a substantially homogenous mass of particles of a solid material, the reciprocating compressor having its intake connected to the discharge side of the rotary compressor, the reciprocating compressor comprising a cylinder, a piston in the cylinder, a flat valve seat on the head of the piston, a resilient suction valve having a spherical curvature adapted to flatten out so as to engage said flat valve seat, ports in the piston head communicating with the interior of the cylinder, and means maintaining the valve in functional relationship With respect to the valve seat for intermittent seating on the valve seat.

2. A multistage compressor comprising a reciprocating compressor and a centrifugal compressor, a crankcase for the reciprocating compressor, a rotor for the centrifugal compressor in the crankcase, a rotatably driven shaft in the crankcase for operating both the reciprocating compressor and the centrifugal compressor rotor, a central chamber in the rotor forming a primary intake side and being sealed from the crankcase and adapted for connection to a source of fluid to be compressed, and radial passages extending from the central chamber to the periphery of the rotor, said passages being in the form of interconnecting voids within a substantially rigid porous material, the reciprocating compressor having its intake communicating with the crankcase.

ALLEN TRASK.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 578,860 Clark Mar. 16, 1897 1,797,803 Spreen Mar. 24, 1931 1,889,247 Kenyon Nov. :29, 1932 1,935,538 Bauman NOV. 14, 1933 1,973,103 Replogle Sept. 11, 1934 2,095,842 Steenstrup Oct. 12, 1937 2,272,746 Holm-Hansen Feb. 10, 1942 

